Parabolic concentrators must track the sun and do not collect diffuse light, which can be up to 40% of the available light. Diffuse light concentrating (DLC) type or compound parabolic concentrator (CPC) type collectors potentially increase collector efficiency and reduce the receiver's size and cost by the aperture/receiver ratio or concentration factor, reducing a thermal receiver's heat loss area. However, current designs have poor optical and or thermal performance and require costly and complex manufacturing and materials and or use nonstandard Photovoltaic (PV) cell size, often configured so that frame elements shade PV cells that in turn shut off a line of connected cells.
U.S. Pat. No. 3,923,039 to Falbel described a radiant energy trap with a “plate” receiver. Falbel's receiver does not take full advantage of a bifacial receiver and uses a “scoop” reflector with first and second merging curves formed by respective radii of curvature. The concept of a parabolic second curve is shown in Winston's patents, such as U.S. Pat. Nos. 3,957,031, 4,002,499, 4,003,638, 4,359,265, 5,289,356, 5,537,991, and 6,205,998. The collectors disclosed in the Winston patents are variations on the classic CPC, which suffer from a high (expensive) ratio of reflector curve length to aperture length, having monofacial, bifacial or circular cross-section receivers, where the first curvature accommodates the receiver shape in various ways.
U.S. Pat. No. 6,294,723 to Uematsu sought to increase the angle of acceptance of radiant energy by using a refractor, within which is a bifacial receiver and reflector having a first round curvature and second flat reflector section. The refractor made the collector complicated and expensive to manufacture, without taking full advantage of a bifacial planar receiver.
The author's U.S. Pat. No. 8,207,482 takes full advantage of a bifacial receiver, within a reduced size, heat loss and cost refractor with an external reflector having a reduced reflector curved length to aperture length, but it is still somewhat complicated and expensive to manufacture.
DLC type collectors can be designed to be seasonally load adapted (SLA), which reduces off heating season collector overheating by shaping the reflector to cut off part of the reflected light to the receiver, due to a seasonal increase in the sun's altitude above the horizon. This is discussed in Adsten's 2002 Uppsala University thesis (“Solar Collectors at High Latitudes”), Furbo, Shah and Jordan's 2003 Technical University of Denmark report (“Solar Energy: State of the Art”), and U.S. Patent Publication No. 2010/0243019 to Larsson (mentioned as a hot water and or PV cell solar collector).
An SLA collector for heating buildings can have a relatively small angle of acceptance of radiant energy, which can increase concentration (efficiency). A collector designed for heating buildings allows for a lower collector operating temperature than for heating hot water, which reduces heat loss, but still allows for hot water pre-heat, which is what most hot water collector systems really do. Hot air collectors can avoid heat exchanger system loss by directly heating the air in a building. Overheated air is potentially less of a problem than overheated water. An SLA hot air collector could potentially allow systems to be designed for more than 50-60% annual heat load. On a volume basis, water transfers over 3000 times more heat than air. For this reason, existing flat panel hot air collectors, such as those described in U.S. Pat. No. 4,512,333 to King, U.S. Pat. No. 4,342,307 to Tuck, and U.S. Pat. No. 4,258,697 to Flagg, need the entire aperture area for their mono-facial receiver, with turbulent flow baffles or the like, to achieve a modicum of heat transfer. For this reason, existing hot air collectors have not been able to satisfy the design needs of DLC type collectors with reduced size receivers.
Conventional collector mounting systems patents, such as those described in U.S. Pat. No. 9,628,019 to Atcha, U.S. Pat. No. 9,571,031 to Cavieres, U.S. Pat. No. 9,479,110 to Patton, U.S. Pat. No. 9,309,910 to Anderson, U.S. Pat. No. 9,196,755 to Wildes, and U.S. Pat. No. 8,650,813 to Botkin mention the use of near vertical wind deflectors at the back side of the collector as part of a collector mounting system, to reduce back side wind lift, for low tilt angle (3° to 20°) solar electric panels. However, high tilt angle building heating collectors need more wind protection and may need to spread their roof load over a significantly wider area.